1. Field of the Invention
The present invention relates to reproducing data from an optical storage medium, and more particularly, to an apparatus which detects data recorded on an optical storage medium using a multiple detector so as to guarantee a stable reproduction of the data.
2. Description of the Related Art
FIG. 1A shows a binary signal recorded on an optical storage medium (not shown). FIG. 1B shows the shape of pits recorded on the optical storage medium. FIG. 1C shows an example of an actual radio-frequency (RF) signal read from the optical storage medium.
Generally, the binary signal is recorded as the pits on a surface of the optical storage medium using a laser beam. During a reproduction of data from the optical storage medium, a signal, i.e., a pickup signal, which is detected from the surface of the optical storage medium using a pickup device, must be filtered by a low-pass filter to account for optical frequency characteristics of the laser beam and a reading circuit. Therefore, the RF signal read from the optical storage medium does not have the same form as the binary signal originally recorded on the optical storage medium.
FIG. 2A shows a conventional signal detecting circuit used with a conventional optical storage medium 20. A signal from the conventional optical storage medium 20 is detected using a pre-processor 200 and a detection circuit 210. The pre-processor 200 processes, i.e., filters, a pickup signal read from the optical storage medium 20 and outputs the processed pickup signal as an RF signal. The detection circuit 210 converts the RF signal output from the pre-processor 200 into a binary signal and outputs the binary signal.
There are various types of circuits and methods to restore the RF signal to an original binary signal. For example, FIG. 2B illustrates a conventional detection circuit 210, which uses a slicer as a detector, that is included in the circuit of FIG. 2A.
The detection circuit 210 includes a comparator 211 and a filter 212. The comparator 211 compares an RF signal output from the pre-processor 200 with a signal of a predetermined slicing level. Then, the comparator 211 converts the RF signal into a binary signal by outputting a high level where a level of the RF signal is higher than that of the slicing-level signal, and by outputting a low level where a level of the RF signal is lower than that of the slicing-level signal. The filter 212 is a low-pass filter that filters an output of the comparator 211 and outputs a binary level.
Where an RF signal passes through the comparator 211 and is converted into a binary signal, it is important to appropriately determine a reference level, i.e., a slicing level, of the comparator 211. The slicing level is obtained by passing the binary signal output from the comparator 211 through the filter 212, i.e., the low-pass filter, and making the level of the binary signal to be equivalent to a DC component of the binary signal. Then, the RF signal is compared with the determined slicing level. Based on the comparison result, a binary signal is derived. Such a slicer detection circuit is commonly used to convert a signal read from an optical storage medium into a binary signal.
In addition to the above method, there are other methods of detecting and converting an RF signal into a binary signal. However, various types of optical storage media have been developed recently, and for many reasons, an RF signal is easily distorted. Accordingly, an apparatus and a method of obtaining a binary signal of a good quality from the RF signal are required.